Apparatus for heating fluids, such as air supplied to an indoor space or water for domestic use, are well known in the art. Combined apparatus for simultaneously heating fluid and producing electrical power are also known in the art. Such combined apparatus operate on the principle of converting at least some of the heat energy to mechanical energy to operate an electrical generator. Such apparatus typically include a gas turbine and an electrical generator that is mechanically linked to the turbine. Gaseous products of combustion are used to operate the turbine, which in turn operates the generator to produce electricity. Examples of such combined apparatus are shown and described in U.S. Pat. Nos. 5,148,670 and 6,663,011.
In prior art combustion turbines, operating on a Brayton cycle, air in excess of what is needed for combustion is introduced into the system in order to cool the products of combustion entering the turbine. Typically, this dilution air is about three times what is needed for combustion. However, in residential applications, the air intake and discharge flue are not large enough to accommodate such large amounts of excess air, so that the use of a turbogenerator to convert heat to electrical power is not practical for residential applications using prior art systems.